1. Field of the Invention
The present invention relates to fiber and fabrics made from such fiber material, and particularly fibers and fabrics made from expanded polytetrafluoroethylene (PTFE).
2. Description of Related Art
Since the development of the invention of U. S. Pat. No. 3,953,566 to Gore, flexible fibers made from expanded polytetrafluoroethylene (PTFE) have been used for a variety of purposes, including as a fiber used as a thread and as a component in woven fabrics. These fibers and the fabrics incorporating them have a number of substantial improvements over previous materials. For example, expanded PTFE fibers are chemically inert, are resistant to high temperatures, have high tensile strength, have a high dielectric constant, and are highly lubricious. Additionally, these materials can be treated to impart other desirable properties, such as being filled to provide thermal and/or electrical conductivity.
One of the problems with expanded PTFE materials is that they tend to be difficult to process and they can have a number of structural problems. For instance, unlike some yarns and fibers used for weaving, such as nylon or polyester formed from multiple filaments twisted into a fiber with uniform dimensions, expanded PTFE fibers have generally been formed from a thin, flat tape slit into single filament strands and then folded prior to the spooling process. This folding process is difficult to control during processing and to maintain in the final product, thus resulting in a fiber with inconsistent width and thickness along its length. Also, it has been believed that leaving thin edges of expanded PTFE fiber exposed during processing can cause the fiber to fibrillate.
In an attempt to address some of these concerns, a number of alternative expanded PTFE fiber constructions have been attempted. Folding and/or twisting the expanded PTFE fiber can significantly reduce its tendency to fray or fibrillate. Unfortunately, these processing steps are often difficult to perform while maintaining uniform width and thickness dimensions. Moreover, for certain applications where a very flat weave is desired, these alternative processing steps have been relatively unsuccessful in delivering a suitable product.
Presently, other polymeric fibers have been used to produce flat weave fabrics, such as polyester fiber. Although the proper woven structure can be created in this manner, these other materials simply do not supply sufficient release properties and chemical inertness to allow them to be used in more demanding applications. Another approach to producing a flat weave fabric with improved release properties has been to supply a fluoropolymer coated fiber. This can provide significant improvement in at least initial operation, but performance tends to diminish substantially over time due to coating abrasion, nicks, or delamination. In particularly harsh or demanding applications, such diminished performance simply cannot be tolerated.
Accordingly, it is a primary purpose of the present invention to provide a flat fiber suitable for weaving into a fabric that can be used in harsh environments.
It is a further purpose of the present invention to provide a flat woven fabric that has good release properties, preventing the adhesion of materials.
It is another purpose of the present invention to provide an expanded PTFE fiber material of uniform width dimensions which retains these uniform width dimensions when woven into a fabric.
It is still another purpose of the present invention to provide an expanded PTFE fiber for use in a fabric that is not folded or twisted prior to or during weaving while being resistant to fraying, fibrillation, and shredding.
These and other purposes of the present invention will become evident from review of the following specification.